1. Field of the Invention
The present invention concerns a gantry for a computed tomography apparatus of the type having a rotary carriage that is rotatable around an axis and a support ring arranged around the rotary carriage with a circumferential cooling channel. The invention furthermore concerns a computer tomograph having such a gantry and a method for cooling such a gantry.
2. Description of the Prior Art
In a computed tomography apparatus three-dimensional slice images of the inside of a patient are generated by x-ray imaging method. For this purpose, two-dimensional x-ray slice images, from which a three-dimensional slice image is reconstructed, are generated by a scanning unit that normally includes an x-ray radiator rotating around the acquisition subject and an image acquisition system. The computed tomography apparatus typically has a stationary part that with a support ring is arranged around a patient acquisition space and a supporting body for the support ring. A rotatable rotary carriage that carries the x-ray radiator and an oppositely-situated x-ray detector is supported on the support ring. The combination of the rotary carriage together with the support ring is typically called a gantry.
A problem in such a computed tomography apparatus is the dissipation of the heat that accumulates in the x-ray radiator and the x-ray detector, because 99% of the energy used to generate an x-ray is converted into heat. Local air cooling, for example by means of a ventilator, cannot be used or can be used only in a limited manner in a computed tomography apparatus. The supply and discharge of a gaseous or liquid coolant by means of rigid or flexible coolant lines cannot be accomplished or can be accomplished only in a complicated manner, because of the necessity of not impairing the rotational capability of the gantry.
The cooling systems conventionally used in such computed tomography apparatuses generally include a number of heat exchangers that are installed inside the support ring. In order to efficiently dissipate heat accumulating at the rotating x-ray radiator from the inside of the rotary carriage, a heat exchanger that rotates with the rotary carriage is conventionally mounted in the immediate proximity of the x-ray radiator. This heat exchanger emits heat to the surrounding air. The heated air can be cooled, for example, by a second heat exchanger that dissipates the heat acquired from the air to a cooling system outside of the support ring.
An alternative concept for a cooling system is described in DE 103 12 253 A1, in which the components arranged in the gantry are cooled by compressed coolant air. The compressed coolant air flows via a nozzle ring into a rotatable rotary carriage, the nozzle ring having exhaust openings directed radially outwardly along its entire circumference. The heated air arrives via flow-through openings into a support ring and ultimately escapes outward into the coolant channel via exhaust openings.
A disadvantage in such embodiments that require a transition of the coolant air between the rotating part and the stationary part of a computed tomography apparatus is that unwanted high pressure fluctuations (and consequently noise stress for patient and operator) occur given flowing coolant air and simultaneous rotation.